The big difference is that PIV sex is forbidden by her husband and the OP has highlighted this as an issue. Lots of people can have PIV sex and choose not to, and that's their choice, it's not someone else choosing for them based on their insecurities.
I'm not convinced I agree. AnotherConfused has said several times that it isn't a massive deal to her. That PIV sex is something that would be nice with C but being without it isn't a huge problem. Even if it is a problem, it seems to be something she's willing to live with to help both her husband and C deal with the relationships they have with her and that she has with the other man.
Her husband has said that this is a limit for him - if she has PIV sex with another man, he will leave her. That's up to him, surely? He has absolutely no obligation to be okay with his wife having PIV sex with other men. That may not be something he is willing to work on.
C doesn't want to think of himself as a marriage wrecker and if the marriage dissolved because of sex with him, he would consider himself that way and would end the relationship with AnotherConfused. Up to him. He's being clear about his limits too.
Anotherconfused is asking for advice about what she can do to enhance sex with her husband. That would seem to me to be a much easier thing to do than to convince her husband to get over his problem with her having PIV sex with C and to convince C to get over his discomfort with seeing himself as a marriage wrecker.
In her shoes, I'd seek help for how to work on my own desire for sex with my husband too - because it's easier to work on things that are my own to deal with than convince others to deal with things that are important to me but not to them.
I wouldn't be in her shoes in the first place, though. I wouldn't get married or have children and as I see relationships as non-fixed, if I wanted other partners and my partner wasn't at all comfortable with that, I would seek to change our relationship first - shift it into friendship or dissolve it completely - before seeking to find other partners.
The notion of keeping somebody to be in a romantic relationship with me while I regularly do something that they dislike so much just doesn't appeal to me. For me, no relationship is worth the guilt.
But in Anotherconfused shoes, I'd try to work on my own problems with desire for my husband and that's what she's asked for help with not a debate about her choices.
I just am kind of fascinated that only PIV sex seems to trigger this response. People on here have many agreements with different partners regarding sex. Some only don't use condoms with one partner and use them with all others - mostly for health reasons but I bet there are some folk who do it to keep a nervous partner happy even though they are convinced that their other partners are safe.
Some only engage in anal play with one partner to keep it special. For others it's other things.
Nobody ever seems to get up in arms about those agreements. Only PIV sex seems to trigger this response which I think is a lot to do with how we all conditioned to view sex.
We are not, as a society, terribly sex positive and I think that this notion that the only 'proper' way to have sex is in a way that may result in pregnancy is a reflection of group tendency toward discomfort with sex. Doing sexual things just for fun and just because they feel good isn't enough.
Or at least that's how it seems to me.
IP